1. Technical Field
The disclosure generally relates to gas turbine engines.
2. Description of the Related Art
It is generally acknowledged that gas turbine engines for aircraft and other uses have a tendency to vibrate and generate noise at certain load ratings. To improve engine performance, it is desirable to reduce vibrations by strengthening the components of the engine and increasing the durability of the engine without increasing the weight of the engine. Also, it is desirable to shield the components of the engine from high temperatures where practical.
In the turbine case of a gas turbine engine, there are radially extending struts that are disposed in the path of the hot gases being exhausted from the turbine. The struts extend radially with respect to a longitudinal axis of the engine. The struts extend radially inwardly from the annular turbine exhaust case, through the path of the hot exhaust gases toward the longitudinal axis of the engine to a single axial location that is centrally located on the hub or “torque box.” As such, the struts are disposed in a single plane, positioned at an axial location as measured along the longitudinal axis of the engine. The struts support the hub, which, in turn, supports the bearings of the turbine. The struts, hub, bearings and other components of the engine are constructed in an attempt to withstand the engine vibrations and other load-bearing forces, such as gyroscopic forces and gravitational or G forces.
Because of the extreme heat of the exhaust gases flowing about the struts, it has become common practice to shield the struts from the high temperature and velocity of the exhaust gas by applying fairings about the struts. Typically, the fairings are aerodynamically shaped and tend to divert the hot gases around the struts.
It is desirable to make the struts relatively thick to increase the strength of the struts. However, by enlarging the breadth of the struts, the enlarged struts require more lateral space. The enlarged struts cause the fairings that are adjacent the struts to be larger and the larger fairings tend to apply more resistance to the flow of the hot gases through the turbine section.
It is also desirable to make the struts and the adjacent fairings relatively thin to reduce the drag associated with the fairings. However, by reducing the breadth of the fairings and the associated struts, the strength of the struts is also reduced. Unfortunately, the reduced strength of the struts tends to allow the hub to be more susceptible to the above described forces that may result primarily due to the offset bearing loads carried by the hub.